[Story] Override-able MCP tool descriptions per server #573

Context

Some MCP servers ship tool descriptions that aggressively steer the model — for example, MiniMax's MCP descriptions say the agent MUST use those tools. Users have no way to soften or override these descriptions short of forking the MCP server.

Closes: RooCodeInc/Roo-Code#11738.

Cleaner descriptions also improve search recall for the dynamic tool loading ranker (BM25 and embeddings both rank on description text).

Developer Notes

• Add `toolDescriptionOverrides?: Record<string, string>` to the per-server MCP config schema (`packages/types/src/mcp.ts`). Key: tool name, value: replacement description.
• Apply the override in `getMcpServerTools()` (`src/core/prompts/tools/native-tools/mcp_server.ts`) when composing the API `tools` array — swap in the override before sending, keep the original in the `McpTool` struct for display.
• Show both the original and override descriptions in the MCP settings UI (`webview-ui/src/components/mcp/McpView.tsx`) per-tool edit affordance.

Acceptance Criteria

• `toolDescriptionOverrides` field added to MCP server config schema
• Unit test: override applied when set; no override → original description used
• MCP settings UI shows both original and override; override takes effect on save